An X-ray direct detection CCD (Charge Coupled Device) is an X-ray detector that acquires position information, energy information, and temporal information, etc., of incident X-rays by acquiring an X-ray image by directly capturing X-ray photons by detection pixels of the CCD. Solid-state image pickup elements like this X-ray direct detection CCD (hereinafter, referred to as an X-ray CCD) have excellent position resolution and energy resolution, so that they have been used as standard X-ray detectors in, for example, X-ray astronomical observation satellites (refer to, for example, Patent Documents 1 to 3 for X-ray detectors).